Pharmacokinetics of Sustained-release and Extended-release Buprenorphine in Mice after Surgical Catheterization.

The Guide for the Care and Use of Laboratory Animals strongly encourages the use of pharmaceutical-grade chemicals and analgesics. Sustained-release buprenorphine (SRB) is administered extralabel to rodents to mitigate moderate to severe pain. An FDA-indexed buprenorphine formulation-extended-release buprenorphine (XRB)-has recently become available and is currently the only pharmaceutical-grade slow-release buprenorphine formulation approved for use in mice and rats. However, no studies have directly compared the pharmacokinetic parameters of SRB and XRB in surgically catheterized mice. To this end, we compared the plasma buprenorphine concentrations and pharmacokinetic parameters of SRB and XRB in mice after surgical catheterization. We hypothesized that mice treated before surgery with SRB or XRB would have circulating buprenorphine concentrations that exceeded the therapeutic threshold for as long as 72 h after surgery. Male and female C57Bl/6J mice were anesthetized, treated with a single dose of either SRB (1 mg/kg SC) or XRB (3.25 mg/kg SC), and underwent surgical catheterization. Arterial blood samples were collected at 6, 24, 48, and 72 h after administration. Weight loss after surgery (mean ± SEM) was similar between groups (SRB: males, 12% ± 2%; females, 8% ± 2%; XRB: males, 12% ± 1%; females, 8% ± 1%). Both SRB and XRB maintained circulating buprenorphine concentrations above the therapeutic level of 1.0 ng/mL for 72 h after administration. Plasma buprenorphine concentrations at 6, 24, and 48 h were significantly greater (3- to 4-fold) with XRB than SRB, commensurate with XRB's higher dose. These results support the use of either SRB or XRB for the alleviation of postoperative pain in mice. The availability of FDA-indexed XRB increases options for safe and effective pharmaceutical-grade analgesia in rodents.